1. Field of the Invention
The invention relates generally to the field of carbon tips. More particularly, a preferred implementation of the invention relates to carbon tips with expanded bases. The invention thus relates to carbon tips of the type that can be termed expanded base.
2. Discussion of the Related Art
There are many technological/scientific tools and devices that utilize sharp tips with high aspect ratio. They include scanning probe microscopy, biological probes, field emission (FE) devices, etc. Tip requirements for the above applications include extreme sharpness and a high aspect ratio, combined with mechanical stability as well as chemical inertness and resistance to sputtering. The preferred tip shape is a cylinder because it enables higher resolution when measuring high aspect ratio features and also provides a substantially higher field enhancement at the apex of the tip as compared to other geometries, thereby enabling field emission of electrons at low applied fields.
Vertically-aligned carbon nanotubes (VACNTs) and nanofibers (VACNFs) are materials that possess a number of unique properties that make them well suited for the use as tips. First, VACNTs and VACNFs have intrinsically small diameters (˜1 nm for single-wall CNTs). Second, VACNTs/VACNFs have very high aspect ratios and cylindrical shape. Third, VACNTs/VACNFs exhibit high mechanical strength and flexibility. Fourth, some VACNTs and all VACNFs are electrically conducting which permits their use when current measurements and electron field emission are involved (scanning tunneling microscopy, FE (field effect) devices, biological probes). Fifth, VACNTs/VACNFs are chemically inert and highly sputter resistant. Finally, VACNFs can be grown at predetermined locations (deterministic growth), which enables their incorporation into actual devices.
The growth process of forests of randomly placed vertically aligned carbon nanofibers (VACNFs) was first pioneered by Ren et al. (1). Later on, our group (2) and Ren et al. (3) independently developed a method for deterministic growth of individual VACNFs.
However, there is a significant obstacle associated with the use of high-aspect-ratio cylindrical tips. As the aspect ratio increases, the very ends of these tips exhibit significant thermal and mechanical vibrations. Therefore, what is needed is a solution that provides a high-aspect-ratio cylindrical tip that is thermal and mechanical vibration resistant. What is also needed are carbon tips having improved quality and reduced cost.